In mediolateral oblique view (MLO) the image is taken from an oblique or angled view. During routine screening mammography, the MLO view is preferred over a lateral 90-degree projection because more of the breast tissue can be imaged in the upper outer quadrant of the breast and the axilla (armpit).
The present invention introduces a new compression apparatus and compression paddle to obtain better leveling of the breast tissue in MLOs, and fully taking advantage of the image field in tomosynthesis, which is three-dimensional x-ray imaging.
In x-ray imaging, in particular tomosynthesis, the image field is not shaped as a box. A typical shape is rather a section of a cone with a rectangular cross-section. One problem for the compression paddle edge path with respect to the x-ray field is that the compression paddle is normally wider than the ray field. The width of the field from the x-ray source increases with respect to its height with increasing base section, because the x-ray source scans from one side to the other side.
If the object (breast) is thick, the paddle must be higher up in the x-ray field, where the field is wider. Consequently, the paddle must be wider than the widest field boundary to avoid intersecting of the image. If the object is thin, the paddle will extend outside the object board when it is lowered close to the board.
This is not a problem in CC-positioning, i.e. the patient is standing and the table is horizontal. The problem occurs when positioning with angled examination table, MLO, which may have an angle of 45-60 degrees, to be able to imagine pectoral muscles.
US 2006/0262899 discloses a compression paddle comprising a paddle base, a paddle wall comprising a first side-wall, and a second side-wall. The first side-wall and/or the second side-wall are disposed upon the paddle base and inclined with respect to the paddle base at an angle that is effective to permit an x-ray beam uninterrupted access to an object of interest located on an opposing side of the paddle base from an x-ray source when an angle between a central axis of the x-ray beam and a vertical taken at an inner surface of the first side-wall and/or the inner surface of the second side-wall is about 15 degrees to about 75 degrees. Although the breast compression paddles are for use in mammography systems, including standard and tomosynthesis mammography systems, the invention does not solve all the problems, especially related to MLO, in particular for tomosynthesis.